As for slash, funnily enough, the first fic I read on FF.net snuck a Coulson/Barton pairing in without any buildup or warning whatsoever. It has some interesting and some spot on dialogue, humour and characterisation but oh, so spotty and bad storytelling technique at other times.

But that pairing did take me by surprise just because of the aforementioned reason.

You seem to have stumbled into PWP territory with that fic. There is plenty of decent fan fic out there, you just have to know where to find it. And not all of it is slash, either. Just most of it.